Research For Textured Glass Substrate With High Efficiency In Light Trapping And The Application In Thin Film Solar Cells

Thin film solar cell structure can be generally grown on glass substrate with low cost. This kind structure can be realized by large area via using PECVD or sputtering method. Compared with bulk silicon solar cell, thin film solar cell has advantage of large area manufacturing with low cost. Photons cannot be fully absorbed within less than 2μm thickness in the absorption layer. But absorption layer of thin film solar cell is generally hundreds of nano- micron thickness. Thus, light absorption rate of flat thin film solar cell is not high, especially for l-band photons which has low absorption coefficient in the limited light path of thin film absorption layer. It seems important to enhance the light absorption of l-band photon in the thin film absorption layer.In order to improve absorption rate of the photons in the membrane structure, low surface reflection and longer light path are usually considered. Light diffraction needs to be enhanced to prolong the light path, especially higher order diffractions. Haze is the percentage of the diffuse light and the light travel through the material, which represents optical transparency of transparent or translucent material as an important parameter. The haze represents light diffraction ability of the membrane structure as well. Micro-nano scattering optical structure has excellent performance of light trapping. The outstanding characteristics have important applications in thin film solar cells. The micro-nano scattering structure on the surface of glass substrate can effectively enhance light trapping for thin film solar cell.After masking and isotropic etching by hydrofluoric acid, glass substrate surface micro-nano structure is shaped in this paper. By applying Rigorous Coupled Wave Analysis(RCWA) method to calculate the function between spectral distribution of haze and the structural parameters, we get the optimized configuration of structural parameters for higher haze distribution. In addition, the relationship of haze spectrum and incident angles is also studied. All these simulation work provides references for the application of the textured glass substrate in thin film solar cell. According to the scallop’s space and haze spectral distribution relationship of hemisphere pit structure, it’s necessary to fabricate the compact hemisphere structure on the surface of glass substrate surface via masking and hydrofluoric acid isotropic etching. In this paper, numerical calculations for compact hemisphere pit structure are made. Applying the Finite Difference Time Domain(FDTD) method on the structure of the compact hemisphere pits, calculation for the transmission field is studied. It is found that compact hemisphere pits structure can effectively diffract vertical incident light. Based on glass substrate with compact hemisphere pits surface, amorphous silicon thin film solar cell is made in the simulation. Applying RCWA method to calculate the light reflectance and absorption rate of the thin film solar cell, optimized structure parameter configuration is achieved. Compared with flat thin film solar cell, the light absorption rate of thin film solar cell based textured glass substrate is improved which provides a reference for the application of textured glass substrate in thin film solar cells.